Updates to data/filesystem classes.
Updates to data/ Interfaces part 1 of 2.
View: clarified that implmentations can change at anytime.\n RefinableView: removed cut and paste errors of word _to_.\nChanged to present tense and active voice, replaced _users_ with _you_.
	modified:   DatasetDescriptor.java
	modified:   DatasetRepositories.java
	modified:   FieldPartitioner.java
	modified:   Format.java
	modified:   Formats.java
	modified:   PartitionKey.java
	modified:   PartitionStrategy.java

Changed to active voice. Replaced "may" with "can." Replaced "will be"
with "is" (everything present tense).
Changed _was_ to _is_ to be present tense, consistent with other exception classes.
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